In order to meet the demand for wireless data traffic soaring since the 4th generation (4G) communication system came to the market, there are ongoing efforts to develop enhanced 5th generation (5G) communication systems or pre-5G communication systems. For the reasons, the 5G communication system or pre-5G communication system is called the beyond 4G network communication system or post long term evolution (LTE) system.
For higher data transmit rates, 5G communication systems are considered to be implemented on ultra-high frequency bands (mmWave), such as, e.g., 60 GHz. To mitigate pathloss on the ultra-high frequency band and increase the reach of radio waves, the following techniques are taken into account for the 5G communication system: beamforming, massive multi-input multi-output (MIMO), full dimensional MIMO (FD-MIMO), array antenna, analog beamforming, and large scale antenna.
Also being developed are various technologies for the 5G communication system to have an enhanced network, such as evolved or advanced small cell, cloud radio access network (cloud RAN), ultra-dense network, device-to-device (D2D) communication, wireless backhaul, moving network, cooperative communication, coordinated multi-point (CoMP), and interference cancellation.
There are also other various schemes under development for the 5G system including, e.g., hybrid frequency shift keying (FSK) and quadrature amplitude modulation (QAM) modulation (FQAM) and sliding window superposition coding (SWSC), which are advanced coding modulation (ACM) schemes, and filter bank multi-carrier (FBMC), non-orthogonal multiple access (NOMA) and sparse code multiple access (SCMA), which are advanced access schemes.
The internet is evolving from the human-centered connection network by which humans create and consume information to the internet of things (IoT) network by which information is communicated and processed between things or other distributed components. The internet of everything (IoE) technology may be an example of a combination of the big data processing technology and the IoT technology through, e.g., a connection with a cloud server.
To implement the IoT, technology elements, such as a sensing technology, wired/wireless communication and network infra, service interface technology, and a security technology, are required. There is a recent ongoing research for inter-object connection technologies, such as the sensor network, machine-to-machine (M2M), or the machine-type communication (MTC).
In the IoT environment may be offered intelligent internet technology (IT) services that collect and analyze the data generated by the things connected with one another to create human life a new value. The IoT may have various applications, such as the smart home, smart building, smart city, smart car or connected car, smart grid, health-care, or smart appliance industry, or state-of-art medical services, through conversion or integration of existing IT technologies and various industries.
Thus, there are various ongoing efforts to apply the 5G communication system to the IoT network. For example, the sensor network, M2M, MTC, or other 5G techniques are implemented by schemes, such as beamforming, MIMO, and array antenna schemes. The above-mentioned application of the cloud radio access network as a big data processing technique may be said to be an example of the convergence of the 5G and IoT technologies.
Recent mobile communication systems are evolving to high-speed, high-quality wireless packet data communication systems to provide data services and multimedia services beyond the initial versions that have provided voice-centered services. Recently there have been developed to support high-speed, high-quality wireless packet data transmission services, various mobile communication standards, such as 3rd generation partnership project (3GPP) high speed downlink packet access (HSDPA), high speed uplink packet access (HSUPA), LTE, LTE-advanced (LTE-A), 3GPP2 high rate packet data (HRPD), and institute of electrical and electronics engineers (IEEE) 802.16. In particular, the LTE/LTE-A system (hereinafter, LTE system) happened to have the maximum frequency efficiency while undergoing continuous development of standards and evolution.
Further, data transmission rate and system capability have been maximized using carrier aggregation (CA) by which the system may be operated via multiple frequency bands. However, the frequency band operated by the current LTE system is the licensed band (the licensed spectrum or licensed carrier) which the service provider generally has a dedicated right to use. Generally, since the frequency band (e.g., a 5 GHz or less frequency band) on which mobile communication services are now being offered is already occupied and used by other service providers or other communication systems, the service provider has difficulty securing and operating multiple licensed bands to expand the system capability.
There are being recently researched techniques to utilize, for the LTE system, the unlicensed band (unlicensed spectrum or unlicensed carrier) relatively easy to secure in order to process mobile data that explosively increases and to address the issue of securing frequency. Among frequency bands in unlicensed bands, particularly the 5 GHz band is used by a relatively small number of devices and allows for utilization of a significantly wide bandwidth. Accordingly, the use of the 5 GHz unlicensed band facilitates to maximize the LTE system capacity.
For example, multiple frequency bands may be utilized based on the CA technique which is one major technology for the LTE system. That is, the LTE cell on the licensed band and the LTE cell (licensed assisted access (LAA) cell or LTE-unlicensed spectrum (LTE-U) cell) on the unlicensed band may be considered the primary cell (PCell (or Pcell)) and the secondary cell (SCell (or Scell)), respectively, to operate the LTE system on the unlicensed band in a manner equal or similar to the legacy CA environment. In this case, the LTE system may be applicable to the dual-connectivity environment where the licensed band and the unlicensed band are connected with each other via a non-ideal backhaul as well as the CA where the licensed band and the unlicensed band are connected with each other via an ideal backhaul.
The orthogonal frequency division multiplexing (OFDM) scheme typically used in the LTE system transmits data via multiple carriers, and this is a sort of multi-carrier modulation scheme that parallelizes symbol sequences inputted in series and modulates the same into multiple multi-carriers, i.e., multiple subcarrier channels with mutual orthogonality and transmits the same.
In the OFDM scheme, a modulated signal is positioned in a 2-dimensional resource constituted of time and frequency. The resources on the time axis are differentiated by different OFDM symbols and they are orthogonal to each other. The resources on the frequency axis are differentiated by different subcarriers and they are also orthogonal to each other. In the OFDM scheme, one minimum unit resource may be indicated by designating a particular OFDM symbol on the time axis and a particular subcarrier on the frequency axis, and this is called a resource element (RE). Since different REs maintain the orthogonality even when undergoing frequency selective channel, signals transmitted via different REs may be received on the reception side without mutual interference.
The physical channel is a channel of a physical layer transmitting a modulated symbol obtained by modulating one or more coded bit streams. The orthogonal frequency division multiple access (OFDMA) system configures and transmits a plurality of physical channels depending on the receiver or the purpose of information streams transmitted. The RE where one physical channel should be disposed and transmitted should be previously agreed between the transmitter and the receiver, and such rule is referred to as mapping.
In the OFDM communication system, a downlink bandwidth includes multiple resource blocks (RBs), and each physical RB (PRB) may include 12 subcarriers arranged along the frequency axis and 14 or 12 OFDM symbols arranged along the time axis. Here, the PRB is a basic unit for resource allocation.
The reference signal (RS) is a signal transmitted by the base station for a user equipment (UE) to perform channel estimation. The RSs for the LTE communication system include the common RS (CRS) and the demodulation RS (DMRS) which is a dedicated RS.
The CRS is an RS transmitted over the overall downlink band and receivable by all the UEs and is used for channel estimation, configuring feedback information by the UE, and demodulation of data channel. The DMRS is an RS transmitted over the overall downlink band. The DMRS is used for demodulation of a data channel by a particular UE and channel estimation, but not used for configuring feedback information unlike the CRS. Accordingly, the DMRS is transmitted through a PRB resource that is to be scheduled by the UE.
A subframe on the time axis consists of two 0.5 msec-long slots, i.e., a first slot and a second slot. The physical dedicated control channel (PDCCH) region that is a control channel region and the ePDCCH (enhanced PDCCH) region that is a data channel region are separately transmitted on the time axis. This is for quickly receiving and demodulating control channel signals. Further, the PDCCH region is positioned on the overall downlink band and this has the form that one control channel is split into smaller units of control channels that are distributed and positioned over the entire downlink band.
The uplink generally comes largely in the physical uplink control channel (PUCCH), which is a control channel and a physical uplink shared channel (PUSCH), which is a data channel. A response signal and other feedback information for the downlink data channel, unless there is a data channel, are transmitted through a control channel, and if any data channel, through the data channel.
Meanwhile, a base station in an LTE cell may communicate with a UE using an unlicensed band in addition to the existing licensed band that it is using. In such case, the LTE cell where the licensed band is available may be denoted as a PCell, and the LAA cell where the unlicensed band is available may be denoted as an SCell.
When the base station uses the unlicensed band, it needs to perform, e.g., a channel occupancy operation appropriate for the unlicensed band. However, the legacy operation of unlicensed band has something inappropriate for the communication characteristics of the LTE cell base station and suffers from the issue that the operation of the base station is not smoothly done on the unlicensed band. For example, although the contention window on the unlicensed band is configured based on a response signal received from one UE, the base station may receive response signals from multiple UEs at the same time which renders ambiguous standards for configuring the contention window. Thus, there is required a method for the base station to smoothly perform communication on the unlicensed band.
The above information is presented as background information only to assist with an understanding of the present disclosure. No determination has been made, and no assertion is made, as to whether any of the above might be applicable as prior art with regard to the present disclosure.